Created attachment 388233[details]
kernel log
I'm seeing this as well.
Host: Fedora 12 + virt-preview
Guest: Fedora 12.
Trying to install Fedora 12 triggers this for me. I get all sorts of strange errors somewhere during package installation, which essentially boils down to I/O problems. Often goes like this: ext4 journal commit error -> filesystem goes readonly -> anaconda bombs out. Sometimes the install manages to complete, the installed system doesn't show normal behavior then though.
Noteworthy data point is that I can install Fedora 11 without any problems, so this is likely connected to some new feature which comes only into play in case both host (qemu 0.12) and guest (kernel > 2.6.31 ?) are new enougth.

In case anyone is still seeing massive numbers of I/O errors with
virtio-blk (even with this patch applied), I don't think this fix is the
whole story. I'm tracking another issue with the alignment of
the user buffer in pread(2) calls here: bug 563103.